114 CHLOROPHYLL. 



benzene, the other, xanthophyll or phylloxanthin, yellow and 

 insoluble. 



These two substances exist, according to Fremy, side by side in 

 chlorophyll. In this opinion, however, he is opposed by Prings- 

 heim and others, 1 who assert that they are only products of its 

 decomposition. Sorby, again, does not consider the existence of 

 a chlorophyll, a phyllocyanin, or phylloxanthin of definite chemical 

 composition to be probable, but rather anticipates in them repre- 

 sentatives of whole series of such compounds. Which of these 

 opinions may be correct it is impossible at the present time to 

 decide. 



Whether the green colouring matters isolated by Filhol, 

 Sachsse, 2 and others, and said to differ spectroscopically from 

 ordinary chlorophyll, are of artificial origin, or whether they can 

 be produced by the plant itself ; what relation probably exists 

 between chlorophyll, ' purified chlorophyll,' or chlorophyllan and 

 cyanophyll ; between xanthophyll, Hartsen's crystalline chryso- 

 phyll and Pringsheim's hypochlorin, are questions involved ii 

 still greater obscurity. 



I restrict myself, therefore, here, to stating that ' chlorophyll y 

 can be extracted from vegetable substances by boiling alcohol 

 after exhaustion with water ; a little, however, is retained by the 

 residue insoluble in alcohol, as benzene still extracts a green 

 colouring matter possessing all the characters of chlorophyll. 3 



1 Chem. Centralblatt, 299, 316, 331, 1880. - Ibid. 121, 1878. 



3 That the chlorophyll exists in different states of combination is rendered pro- 

 bable by the fact that if vegetable substances are exhausted with petroleum 

 spirit, benzene, ether, etc., in succession, each of these solvents removes chloro- 

 phyll, so that when petroleum spirit fails to dissolve more of it, appreciable 

 quantities can still be extracted with benzene. This combination might be con- 

 ceived to be simply mechanical, the protoplasm acting in a similar manner to 

 hydrate of aluminium which, as is well-known, has the power of mechanically 

 retaining chlorophyll. But the question may also be raised whether chlorophyll, 

 which, in the opinion of many authors, possesses the characters of a weak acid, 

 does not exist in plants in combination with different bases, and whether 

 soluble (basic) alkali-compounds, such as those artificially produced by Freiny, 

 do not occur ready-formed in some plants. Every one that has been frequently 

 engaged in plant-analyses must have observed that well-filtered aqueous 

 extracts of leaves, etc., when acidified and shaken with benzene or ether, yield 

 to those solvents substances which on evaporation assume a green tinge and 

 possess all the characteristic properties of chlorophyll. The assumption of the 

 presence in the aqueous extract of a colourless chromogene converted during 

 the successive operations into chlorophyll would, it is true, be possible, but I 

 cannot as yet regard the first view as untenable. The whole subject, indeed, 

 appears to me deserving of further investigation. 



